Most dances are 32 bars (64 steps) long, and repeat. They generally involve moving around a bit and ending back up where you started, then a progression (if there is one), which is where the dancers move round so they're dancing with different people or in different positions. The progression usually takes place in the last 8 bars, and ends with a swing (which is catch-up / get ready to do it all again time).
Circle - everyone in a circle, partner by your side.
Longways Set - everyone in a long line down the room, opposite their partner. Can be a fixed number of couples (e.g. 6) or as many as can fit ("as many as will").
Sicilian Circle - couple facing couple around the room, one couple facing clockwise round the room, one facing anti-clockwise.
Square – four couples in a circle, with 2 couples (the Heads) facing up and down the room, and 2 (the Sides) facing across.
Commonly 32 bar reels or jigs (both of which have two beats or steps to the bar). The 32 bars are made up of 4 x 8 bars in a pattern AABB - i.e. 8 bars played then repeated, then a different 8 bars played then repeated. The sets of 8 bars are known as A1, A2, B1, B2. Dances with gallops in them work better with Jigs.
There are CDs produced by well known ceilidh bands that are specifically designed for dancing to - see the resources section. Other tracks that work are Rednex - Cotton Eye Joe and Sham Rock - Tell Me Ma. Music usually has an introduction of 4 or 8 bars to allow dancers to get feel of the speed and rhythm.
The music structure is important because most barn dance moves (circle, star, dosido...) take 4 or 8 bars.
Calling consist of “walking through” the dance (explaining what to do without music) and then calling out the dance moves while the music is playing. The golden rule is "call the move before the phrase of music starts". I find the easiest way to learn to do this is to count the steps out loud, and then to replace the last few steps with the next instruction, so go from "1 - 2 - 3 - 4 - 5 - 6 - 7 - 8" to "1 - 2 - 3 - 4 - 5 - 6 - Circle - Left"
Lucky 7 (keep your partner version) instructions – circle, 32 bar reel
Circassian circle instructions / video - circle, 32 bar reel. Don't force them into boy-girl couples, but still have the girls go in then the boys.
Triple Time instructions / video - longways sets for 7 to 10 couples, 32 bar jig (make sure everyone gallops at least once each time)
OXO Reel instructions - 6 couple longways, 32 bar Jig. OXO means the top two couples Circle Left and Right while middle two couples Right Hand Star and Left Hand Star while the bottom two couples Circle Left and Right. Can do with 7 couples (middle 6 do the stars) or 8 (circle, star, circle, star).
Thread the Needle instructions - Longways sets of 5 or 6 couples, 32 bar Reel
Old Swan Gallop instructions / video – Sicilian Circle, 32 bar Jig
Cornish 6 hand reel instructions / video – line of 3 couple across the room, all facing down. Although this has quite complicated stuff, it has the advantage of you always end up back with your partner in the same place after each section. Don't be afraid to replace the reel with just walk to each side and back. It’s a 64 bar dance, so use a 32 bar tune with an even number of times through, or use the classic from the Oysterband (http://www.virginmedia.com/music/browse/oysterband/songs/257542)
Cumberland Square 8 instructions / video – 64 bar dance, so use a 32 bar Jig an even number of times through
Scatter Promenade instructions – circles of 4 people (2 couples) scattered around the room, 32 bar Jig.
Bismarcks: Upstream (http://www.rootsrecordsonline.co.uk/products/6460) and Joanna
Committee Band: It’s About Time and Dance Music (available on a double CD: http://www.committeeband.co.uk/)
Peeping Tom: A sight for sore eyes (http://www.amazon.co.uk/A-Sight-For-Sore-Eyes/dp/B0016B1WI6), The Eyes have it, Looking Good (http://www.rootsrecordsonline.co.uk/products/5672), Looking Back (http://www.rootsrecordsonline.co.uk/products/5278)
These CDs all have very clear phrasing which helps both the caller and the dancers.
Jeremy Child http://www.barndancecaller.net/